1. Field of the Invention
This invention is directed to the quantitative determination of properties of geologic materials and, in one aspect to the quantitative determination of the hydration behavior, including swelling stress and swelling pressure, of materials such as shales; and particularly the effect of different fluids on such materials.
2. Description of Related Art
Wellbores can become destabilized for a variety of chemical and mechanical reasons. A study of a sample core from a wellbore can reveal properties of the formation in which the well is located. These properties can indicate both chemical and mechanical causes of well destabilization and possible cures which will stabilize the wellbore. A variety of drilling fluids have been used to overcome destabilizing chemical mechanisms and mechanical mechanisms.
Shales are formations with high clay contents that are subject to hydration, swelling and reduction in compressive strength upon exposure to water. Shale formations make up a high percentage of the intervals drilled and cause most of the wellbore stability related problems. Confined shales upon exposure to low salinity water can develop very high swelling pressures. Inhibitive drilling fluids are often required to prevent wellbore destabilization due to shale hydration.
There is a great need for methods and apparatuses to accurately and quantitatively measure the hydration and swelling behavior of shales when exposed to different drilling fluids. Shales make up over 75% of drilled formations and often cause over 90% of wellbore stability problems and the associated stuck pipe. Choosing properly inhibitive drilling fluids for particular shales is a very difficult and uncertain task. The swelling pressure generated by a shale in the borehole wall upon exposure to a fluid has a great impact on the relative weakening of the shale and possible wellbore failure. Quantitative swelling pressures of preserved shales have not been measured in prior work.